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Longest Stitch and Glue Boat

I am interested in building a very long stitch and glue open boat. I am thinking LOA of between 30 and 36 ft and a beam of no more than 7ft. Has anybody built a stitch and glue boat of this size? Does anybody have any thoughts or ideas about possible ply thickness needed or possible problems when building a stitch and glue boat of this size ?

Re: Longest Stitch and Glue Boat

... Does anybody have any thoughts or ideas about possible ply thickness needed... when building a stitch and glue boat of this size ?

The ply thickness needed is the thickness the designer says to use.

There is no rational, logical, or physical description of how free will could exist. It therefore makes no sense to praise or condemn anyone on the grounds they are a free willed self that made one choice but could have chosen something else. There is no evidence that such a situation is possible in our Universe. Demonstrate otherwise and I will be thrilled.

Re: Longest Stitch and Glue Boat

Thanks JimD. I have built a 16 ft Selway Fisher Power 1 in the past. I think I used 9mm ply for the floor and 6mm on the sides as recommended by designer. I was thinking of building the same design, but doubling the length. My thoughts are that it would be OK to stick with the same thicknesses as long as there were plenty of built in seats/buoyancy epoxied into the hull to create stiffness. Just wonder if anybody has any other thoughts.

Re: Longest Stitch and Glue Boat

Originally Posted by Hudson Marine Internation

Thanks JimD. I have built a 16 ft Selway Fisher Power 1 in the past. I think I used 9mm ply for the floor and 6mm on the sides as recommended by designer. I was thinking of building the same design, but doubling the length. My thoughts are that it would be OK to stick with the same thicknesses as long as there were plenty of built in seats/buoyancy epoxied into the hull to create stiffness. Just wonder if anybody has any other thoughts.

With the caveat that I am not a naval architect and have absolutely no qualifications in this area, I'd be cautious about increasing the length by that much. Strike that. Not just cautious. I think that's a really bad idea. I've heard of stretching a design by 10%-20% or so, but going from 16' to over 30' is a huge change. Just for a start, I'm certain that your scantlings for the 16' design are nowhere near adequate for the larger boat.

There are plenty of v-bottom, stitch & glue skiff designs out there. It's worth looking for one that meets your criteria rather than trying to adapt the Power 1 design. For example I suspect that it would be far easier to adapt the Selway Fisher Power 4 design to an open skiff (assuming that's what you are looking for). It's also worth looking at that design to see how a naval architect would approach the project of designing a larger boat. I think you will quickly see that the changes go far beyond simply increasing the length.

Re: Longest Stitch and Glue Boat

Re: Longest Stitch and Glue Boat

Skin thickness is usually determind by frame spacing and displacement. Can you build a boat that long from 9mm, yes, but how much weight do you intend to put in it?
I have plans for one of the Power series, having straight sections aft. does allow for easy extension, i have discussed this with Paul, but not as much as you are thinking about.
There is nothing written in stone about how much a design can be stretched, it depends on the original design. One example, a narrow beam 6ft 6in canal boat, built on the same mid section in lengths from 20ft to 75ft.

Re: Longest Stitch and Glue Boat

I think it could be done. Although they are not built stitch and glue, I would copy the bulkhead spacings and ply thicknesses from one of Bolger's power sharpies. These boats were designed to be built as lightly as possible, have similar beam/length ratios to what you are thinking of, and seem to be strong enough in sheltered waters and on a trailer. I think the "tenesee" is around the length you mentioned. Good luck.

Re: Longest Stitch and Glue Boat

Originally Posted by skaraborgcraft

Skin thickness is usually determind by frame spacing and displacement. Can you build a boat that long from 9mm, yes, but how much weight do you intend to put in it?
I have plans for one of the Power series, having straight sections aft. does allow for easy extension, i have discussed this with Paul, but not as much as you are thinking about.
There is nothing written in stone about how much a design can be stretched, it depends on the original design. One example, a narrow beam 6ft 6in canal boat, built on the same mid section in lengths from 20ft to 75ft.

The beauty of the stitch and glue method when making the likes of the Power1 from Selway Fisher is that the hull and the seats form a monocoque structure. I did not use any frames on my Power 1. It is very stiff and tight even after a couple of decades and has taken a good thrashing in different conditions.

Re: Longest Stitch and Glue Boat

Originally Posted by Al G

I think it could be done. Although they are not built stitch and glue, I would copy the bulkhead spacings and ply thicknesses from one of Bolger's power sharpies. These boats were designed to be built as lightly as possible, have similar beam/length ratios to what you are thinking of, and seem to be strong enough in sheltered waters and on a trailer. I think the "tenesee" is around the length you mentioned. Good luck.

Re: Longest Stitch and Glue Boat

Almost all of the traditional boats around the world have a much higher LOA to beam ratio than is common in modern boats. The Aussie idea of taxing the boat rego according to the length seems to have influenced the prevalence of short fat stubby boats with massive outboards. I think they should be taxing the outboard HP and not the LOA. Then again, maybe no tax would be a better idea.

Re: Longest Stitch and Glue Boat

HMI, you should ask Paul. Not just about the materials but the design itself. Seriously, you don't want to be guessing about a build that big and expensive. Good luck.

Last edited by JimD; 03-19-2017 at 10:18 AM.

There is no rational, logical, or physical description of how free will could exist. It therefore makes no sense to praise or condemn anyone on the grounds they are a free willed self that made one choice but could have chosen something else. There is no evidence that such a situation is possible in our Universe. Demonstrate otherwise and I will be thrilled.

Re: Longest Stitch and Glue Boat

If not lots of good information in there. I am not looking at in right now, but I think his 20+ range boats use more than 3/8" ply at least on the bottom. You are talking a long boat under power hitting chop, waves, and wakes.

Re: Longest Stitch and Glue Boat

No it is not, it is determined by the stresses caused by the heavy weights acting in a different location to the buoyancy in waves bending the hull in two.

Frame spacing is important in dealing with local loads like wave slap. Scantling sizes are a blend of the two.

According to John Teal....

I think Gerr has a similar formula, but of course, other factors are involved, i used a simple example rather than dive head first into material modulus and shock loadings, which as you point out, are relevant.

Re: Longest Stitch and Glue Boat

If you want to work out the structural design problems yourself take a look at "Elements of Boat Strength" Dave Gerr. If you have a reasonably determined intelligence you can work out the scantlings (size of the structural members as a function of displacement & intended use) yourself. It would take real thought & study because the consequences of failure are...high. But it's very straight forward if you are not afraid to ask questions & are looking for a challenge.

Way more fun than just buying a design..But personally I've become very comfortable working out the construction myself - the design...not so much. The hull shape, balance, stability & performance of something that big are not something I'd suggest for an amateur - the safety & $$$ risks are too high - but how it's built is within the capability of a studious & energetic amateur.

Al G has some excellent advice. Read up on Bolger's work!

I think it could be done. Although they are not built stitch and glue, I would copy the bulkhead spacings and ply thicknesses from one of Bolger's power sharpies. These boats were designed to be built as lightly as possible, have similar beam/length ratios to what you are thinking of, and seem to be strong enough in sheltered waters and on a trailer. I think the "tenesee" is around the length you mentioned. Good luck.

Re: Longest Stitch and Glue Boat

Originally Posted by skaraborgcraft

According to John Teal....

I think Gerr has a similar formula, but of course, other factors are involved, i used a simple example rather than dive head first into material modulus and shock loadings, which as you point out, are relevant.

Those are local loads, not global loads, The formula under those lines will include fiddle factors derived from a "conventional" set of boat proportions and structural layout. Deviate from that family of proportions and you are in a different ball game.
You can start with those, and then calculate the I/y of the hull girder using the thicknesses that they give you to see if the resultant girder is strong enough.
This is for still water inland craft https://www.google.co.uk/url?sa=t&rc...Pvx89Q&cad=rja
Put it on waves and you need to allow for the variation in the buoyancy distribution as well.

Get it wrong and

It really is quite difficult to build an ugly wooden boat.
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Re: Longest Stitch and Glue Boat

Originally Posted by Peerie Maa

Those are local loads, not global loads, The formula under those lines will include fiddle factors derived from a "conventional" set of boat proportions and structural layout. Deviate from that family of proportions and you are in a different ball game.
You can start with those, and then calculate the I/y of the hull girder using the thicknesses that they give you to see if the resultant girder is strong enough.
This is for still water inland craft https://www.google.co.uk/url?sa=t&rc...Pvx89Q&cad=rja
Put it on waves and you need to allow for the variation in the buoyancy distribution as well.

Get it wrong and

Looks to me they just put one too many turns on the fore stay screw! I would have thought "bouyancy distribution" would be factored in to the equation already, and some believe Gerrs formulas are a little on the heavy side, though at the light displacement im usually fumbling around with, his formula generally agrees with Teale .
Am i going to get a wet a**e when i hit the first wave in the "13"?

Re: Longest Stitch and Glue Boat

There are at least four different types of loads acting on a boat hull.

1) Hydrostatic loads, (keeping the water out) the water pressure acting on the outside of the planking.
2) Dynamic Loads, the loads created by speed through the water and slamming into waves.
3) Global loads, the bending of the hull as it travels over waves.
4) Point loads, things like outboards on transoms, fuel tanks, chainplates, ballast, and mast steps for sailboats, etc.

Planking thickness is sometimes only intended to deal with load #1, keeping the water out, and internal framing deals with #2 and 3 and additional structure deals with 4. But in a modern stitch-and-glue (or fillet-and-tape) structure the skin plus the internal furniture (bulkheads and girders) take all loads into consideration.

In a traditional open panga type, there are 5 substantial longitudinal timbers to deal with loads #2 and #3. The rails or clamps, the chine logs, and the keel or apron. In stitch-and-glue you need to duplicate the stiffness added by these longitudinal members. The easy way is with tall deep longitudinal girders (like the seat front) running full length of the hull. Add some bulkheads to tie the boat together across the centerline and you're good. Add cleats on the top and bottom of the light ply girder (making an I-beam) and you're really good.

As Nick said, the general scantling rules by Gerr and Teal are fine if you stick more-or-less to traditional proportions and construction methods, but they do not apply to long, skinny, low sided open boats.

Re: Longest Stitch and Glue Boat

Originally Posted by TR

There are at least four different types of loads acting on a boat hull.

1) Hydrostatic loads, (keeping the water out) the water pressure acting on the outside of the planking.
2) Dynamic Loads, the loads created by speed through the water and slamming into waves.
3) Global loads, the bending of the hull as it travels over waves.
4) Point loads, things like outboards on transoms, fuel tanks, chainplates, ballast, and mast steps for sailboats, etc.

Planking thickness is sometimes only intended to deal with load #1, keeping the water out, and internal framing deals with #2 and 3 and additional structure deals with 4. But in a modern stitch-and-glue (or fillet-and-tape) structure the skin plus the internal furniture (bulkheads and girders) take all loads into consideration.

In a traditional open panga type, there are 5 substantial longitudinal timbers to deal with loads #2 and #3. The rails or clamps, the chine logs, and the keel or apron. In stitch-and-glue you need to duplicate the stiffness added by these longitudinal members. The easy way is with tall deep longitudinal girders (like the seat front) running full length of the hull. Add some bulkheads to tie the boat together across the centerline and you're good. Add cleats on the top and bottom of the light ply girder (making an I-beam) and you're really good.

As Nick said, the general scantling rules by Gerr and Teal are fine if you stick more-or-less to traditional proportions and construction methods, but they do not apply to long, skinny, low sided open boats.

Re: Longest Stitch and Glue Boat

Keep in mind you will need a "qualified" person to sign off on the ABP paperwork before you can obtain the plate and thus be able to register your vessel,it might be easiest to discuss this with your designer if you want his signature on a legal document.Be worth researching the ABP requirements in Queensland.
Cheers,
Dave.

Re: Longest Stitch and Glue Boat

I'm not a naval architect, but I am an engineer, and can hopefully give you some insight as to why this might be a bad idea.

The forces acting on any given area of a boat by waves or other things that primarily touch flat areas are proportional to the AREA of that feature. So, to evenly compensate for the force that would have been exerted on a 1x1 foot typical area of a hull that you are doubling the scale of, you may need up to 4 times the wall thickness (assuming that the distance between structural supports also scales), because 1x1 = 1, but at 2X scale 2x2 = 4

You can probably mitigate that by doubling the supports, but may still need about twice the thickness.

But, the problem gets worse, because any forces that are proportional to the VOLUME of water that the boat displaces, which is a good chunk of the design problem, are multiplied by 8, because 1x1x1 = 1, but 2x2x2 = 8, and you need to consider 3 dimensions when you're dealing with volume.

These are worst case calculations, but in general the main point is that a 3D item scaled up 2X actual yields 8X factors, which is something that people that don't normally think in 3D realize right away. They just figure that if you're making it 2X bigger, then everything is 2X more.

So ... be very, very careful. Buy plans from someone that knows what they're doing.

Re: Longest Stitch and Glue Boat

Originally Posted by DaveBrewer

Keep in mind you will need a "qualified" person to sign off on the ABP paperwork before you can obtain the plate and thus be able to register your vessel,it might be easiest to discuss this with your designer if you want his signature on a legal document.Be worth researching the ABP requirements in Queensland.
Cheers,
Dave.

Ah yes. Suddenly in 2006 we were no longer considered sensible enough to decide for ourselves what size of engine and how many passengers would be sensible.

Re: Longest Stitch and Glue Boat

Originally Posted by mirrordude

I'm not a naval architect, but I am an engineer, and can hopefully give you some insight as to why this might be a bad idea.

The forces acting on any given area of a boat by waves or other things that primarily touch flat areas are proportional to the AREA of that feature. So, to evenly compensate for the force that would have been exerted on a 1x1 foot typical area of a hull that you are doubling the scale of, you may need up to 4 times the wall thickness (assuming that the distance between structural supports also scales), because 1x1 = 1, but at 2X scale 2x2 = 4

You can probably mitigate that by doubling the supports, but may still need about twice the thickness.

But, the problem gets worse, because any forces that are proportional to the VOLUME of water that the boat displaces, which is a good chunk of the design problem, are multiplied by 8, because 1x1x1 = 1, but 2x2x2 = 8, and you need to consider 3 dimensions when you're dealing with volume.

These are worst case calculations, but in general the main point is that a 3D item scaled up 2X actual yields 8X factors, which is something that people that don't normally think in 3D realize right away. They just figure that if you're making it 2X bigger, then everything is 2X more.

So ... be very, very careful. Buy plans from someone that knows what they're doing.

Mirror, as an engineer, what are your thoughts about speed? The impact of hitting a wave at 6 knots versus hitting it at 12 knots verses hitting it at 24 knots ? Does the impact double as the speed doubles or does it increase in a different way ?

Re: Longest Stitch and Glue Boat

Fisher has already extended the Power 1 design to 32'. Albeit with a 10' 9" beam so it's hard to exactly compare it to a 6'ish beam. But he uses a combination of 1/2" and 1" ply for the girder and planking.

Re: Longest Stitch and Glue Boat

Originally Posted by Hudson Marine Internation

Mirror, as an engineer, what are your thoughts about speed? The impact of hitting a wave at 6 knots versus hitting it at 12 knots verses hitting it at 24 knots ? Does the impact double as the speed doubles or does it increase in a different way ?

Kinetic energy is calculated e = ½mv2 where m is mass and v is velocity, so the forces involved as the hull slams into the wave increases by a factor of four as speed doubles, at least theoretically.

This also means that if you go from 6 knots to 24 knots the energy involved increases 16 times, design for top speed seems to be the lesson here...

Re: Longest Stitch and Glue Boat

Reuel Parker builds long narrow plywood boats, using stitch and glue methods. For example, his new Seabright 33 sailboat is 35 feet long and 8.5 foot beam.

For powerboats, a great deal depends upon how much you push them. If you are content to go at 10-15 knots, then engines can be small, and boats can be light.
Phil Bolger's SNEAKEASY is a stiff boxy 27 x 4-foot boat that moves easily with a 20 HP engine. Nigel Irens has been developing a series of round bilge boats with low displacement relative to their length (WoodenBoat 242, Jan-FEb 2015). His own GRETA is 26 feet on the waterline, and does 11 knots with 13 HP.

Of course you can build a light, strong 30-36 foot boat with a beam of 7 feet. These may or may not be ideal dimensions for your purposes.
Do you wish to share with us what you wish to do with your skinny boat?

Re: Longest Stitch and Glue Boat

When you are dealing with plywood, the strength isn't the only factor. The other one is the bendability of the plywood. A longer boat would have gentler curves (not so good for strength but good for bending). Still, you might end up having to laminate the boat from several layers of thinner plywood around the forefoot.

Do get Devlin's book; there is a graph relating thickness of plywood with size of boat and in his book are a lot of examples of larger boats. However, there is no mention in the graph about the internal frames/bulkheads, which are probably more numerous in a larger boat. In most bigger ply boats, and even some small planing sailing dinghies, there is an internal "waffle box" structure under decks, cabins and/or cockpit soles.

Re: Longest Stitch and Glue Boat

You could benefit from looking at where long and skinny works.
These go like the clappers, but on FLAT lake waters.

If you want to go skinny and fast in a sea way, the developments are for wave piercing forms.

Basically a VSV is a wave piercer. It is not completely novel as designers have been developing slim sharp fronted boats for years that are encouraged to cut through the waves rather than bouncing over them. The VSVâ„¢ applies these principles to high-speed patrol vessels. This has enabled crews to travel at high speeds in adverse sea conditions in relative comfort and safety.
Vosper Thornycroft has its own VT Halmatic VSV, 16 m long:

and is developping a 22 m version.

It really is quite difficult to build an ugly wooden boat.
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